Investigation of the influence of progesterone on mouse embryo transport by using antiprogestational steroids.

The rate of embryo transport through the mouse oviduct was unaltered by ovariectomy after ovulation, essentially unaltered by administration of progesterone after ovulation but increased by preovulatory administration of progesterone. The antiprogestational steroid RMI 12,936 caused an arrest of embryo movement when given on Day 1, 2 or 3 of pregnancy and similar, though less marked, delay was caused by R2323, another progesterone antagonist. The effects of RMI 12,936 given on Day 1 were reversed by progesterone administration after a latent period of 24-48 h. These results indicate that the egg transport process in the mouse in triggered by progesterone and requires continued progesterone activity for its maintenance.